1. Field of Invention
The application relates to wireless networks and more particularly to a method of reducing factory test time of receiver sensitivity of a wireless device, such as a Code Division Multiple Access (CDMA) wireless device.
2. Description of the Related Prior Art
As shown in FIG. 1, the delivery end of a typical mobile communication system 100 is divided into a number of cells 110 or geographical coverage areas, within each of which is a base station 120. Alternately, base station 120 for a number of cells 110 is co-located at the intersection of those cells and directional antennas are used to provide coverage over the area of each adjacent cell. Each base station 120 contains radio transmission and reception equipment for communicating with a wireless device 130, such as mobile phone, laptop, personal digital assistant (PDA) or the like, located within the associated cell 110. The coverage area of a given cell 110 is dependent upon a number of factors such as transmit/receive capabilities of the base station 120 and/or wireless device 130, the antenna (not shown) of base station 120, and the topology of the area. Specific radio frequencies are allocated with each cell 110. In a CDMA wireless network, the same frequency is reused in every cell. Each base station 120 connects to a backbone infrastructure (not shown) which perform a variety of functions such as the set up and tear down of call and the handoff of calls from one base station 120 to another.
FIG. 2 depicts a representative CDMA receiver block 200 for wireless device 130. Antenna 210 receives radio frequency signal 220 from base station 120 and converts it into a current on a conductor. The signal is very weak from absorption so, after passing through duplexer 230 (which simply permits a single antenna system to be used for both transmitting and receiving) the signal is amplified in low noise amplifier (LNA) 240. The signal is then passed through filter 250 to eliminate out-of-band noise and interference. In order to recover the original information signal from the modulated radio frequency signal 220, the signal is sent through mixer 260 which is fed by local oscillator (LO) 270 at the same frequency as the one in the transmitter (not shown) of base station 120 if, as shown in FIG. 2, zero intermediate frequency (IF) technology is used. Alternatively, there may be more than one mixer 260 to mix the received signal 220 down to at least one non-zero intermediate frequency and then down to a baseband signal by multiple steps. Out of the mixer 260 come two frequency signals (sum and difference). One of the frequencies is the intermediate frequency, the other is eliminated by filter 280. The resulting signal is amplified by amplifier 290, and passed through analog to digital converter 300 for digital processing in baseband processor 310 which may include a RAKE receiver. As those skilled in the art will appreciate, wireless device 130 is a transceiver in that it incorporates both transmitter (Tx) and receiver (Rx) functionality (e.g. the power amplifier (PA) associated with the transmitter is shown in FIG. 2). As will also be appreciated, the signal processing system of wireless device 130 may be comprised of multiple analog and mixed signal integrated circuit (IC) chips (such as amplifiers, filters, A/D and D/A converters), digital IC chips (such as memory, digital signal processors (DSP), and microprocessors) and many passive discrete components.
Quality assurance measures at the factory level ensure that wireless device 130 operates satisfactorily. Various standards have been developed against which wireless device 130 is measured. One such standard is a Telecommunications Industry Association/Electronic Industries Association standard, TIA/EIA/-98E, which defines recommended minimum performance standards for cdma2000 spread spectrum mobile stations. More specifically, a test is established in this standard for receiver sensitivity and dynamic range. The radio frequency (RF) sensitivity of a cdma2000 mobile station receiver is the minimum received power, measured at the mobile station antenna connector, at which the frame error rate (FER) does not exceed 0.5% with 95% confidence. In CDMA systems, the frame is the basic physical channel data packet, typically having a 20 ms transmission time that consists of information on the traffic channel (voice or data). Because the link between base station and handset is established on a frame-by-frame basis the performance of a CDMA mobile phone is evaluated in terms of its FER. Regarding receiver sensitivity, two sources of interference are purely additive white Gaussian noise (AWGN): the receiver's input-referred thermal noise power spectral density (No) and the transmitter's thermal noise power spectral density (NTx) in the receiver frequency band (see FIG. 2). A typical sensitivity and dynamic range test setup using FER is shown in FIG. 3A while the associated test parameters as defined in TIA/EIA/-98E are shown in FIG. 3B. A sensitivity test (test 1) ensures the receiver's ability to receive weak signals, and a dynamic range test (test 2) ensures the receiver's ability to receive a strong signal. In FIG. 3A, the base station 120 is simulated using a piece of test equipment 320, such as the Agilent 8960 wireless communications test set, which feeds a test signal to an antenna port of a device under test (DUT) 330. As highlighted in FIG. 3B, a typical test, at 9600 bps (RC 1 and 3) or 14400 bps (RC 2) data rate, consists of setting the test parameters of Test 1 or Test 2, and counting the number of frames transmitted at the base station and comparing it to the number of erroneous frames received at the mobile station.
One of the problems with the TIA/EIA/-98E receiver sensitivity test is that the test time is too long for mass production, being physically restricted by the arrival rate of the frames at DUT 330. In an attempt to reduce the test time, the maximum number of frames for the sensitivity test is limited to no more than 1000 (which may not always achieve the required 95% confidence level), but this method still takes up to 80 seconds for four channels at two bands. As will be appreciated, for thousands of units, the test time and associated cost in man hours may become prohibitive.